1. Field of the Invention
The invention relates to rolls such as for glass manufacturing. The rolls can convey hot slabs or sheets, as of glass. The rolls typically comprise a steel mandrel and an insulating refractory cover. The cover may be made from materials including refractory fiber, such as ceramic fiber, or compressed millboard. The end assembly of the roll can maintain the roll in compression.
2. Description of the Prior Art
Insulating materials for use in high temperature applications were historically made from asbestos. A roller conveyor can be made with an inner metal shaft and an outer insulating cover. Asbestos discs can be stacked onto the shaft, and pressed together axially, as discussed, for example, in U.S. Pat. No. 3,802,495. The discs can also be pressed together by hydraulic means as taught in U.S. Pat. No. 3,116,053.
Ceramic fiber has been successfully used as a replacement for asbestos in certain applications. For example, it is taught in U.S. Pat. Nos. 5,205,398 and 5,378,219 to use ceramic fiber as a roll cover. Annular discs of bulk ceramic fiber are stacked onto an inner metal shaft and may be axially compressed at greater than about 50 percent of the fiber's original density. The compressed discs on the metal shaft may be perfused with colloidal silica and dried. The discs are then recompressed and held permanently in compression.
A compression set can be a problem in a refractory fiber roll cover that is held in compression. Compression set is the tendency of a material to shrink under heat and compressive load. Along the axis of the roll, compression set causes the cover to lose its resiliency and rigidity, both of which are necessary to support slabs or sheets.
Prior practice has generally compensated for compression set by stopping production and replacing the affected rolls. Affected rolls can be reconditioned by unlocking the end plate, recompressing the fiber, and locking the end plate. The reconditioned roll is then ready for reuse.
Also, U.S. Pat. No. 5,307,563 teaches a method of making a roll comprising a mandrel covered by a plurality of resin-impregnated, fibrous discs. Threaded washers tighten along the longitudinal axis of the mandrel to compress the fibrous discs until the resin hardens. However, the patent does not describe tightening after hardening of the resin.